If I was writing a story in which there was a character who was an orc who defiled things (god forbid) and I was insane enough to try and construct a generic term for him, I think I’d go for “orcish defiler”, although that risks him being thought of as a defiler who’s a bit like, but not actually, an orc. I definitely wouldn’t go for the hyphenate, though.

A Moria orc-defiler would indeed be a defiler of orcs, by my reading, and not an orc who defiles generally. However he could be a defiler of orcs who just happens to live in Moria – he shouldn’t have to restrict himself to just defiling Moria orcs.